WSU Research Gives Brett a Chill

Combination of temperature and sulfur dioxide shuts down unwanted yeast in wine

by Peter Mitham

Joshua Maloney of Milbrandt Vineyards is interested in ways to control Brettanomyces in the cellar.

Pullman, Wash.—Researchers at Washington State University are giving Brettanomyces the cold shoulder with new research that studies how temperature and sulfur dioxide impact the organism, and how the combination of the two help control its development in wine.

Brettanomyces bruxellensis—the yeast commonly known as Brett—is a scourge of wineries. While the yeast may be naturally present in vineyards, it can produce compounds that impart earthy, barnyard characters to wine.

Most winemakers want to shut the door against its establishment in wineries. Clean equipment helps avoid Brett, but established populations often are controlled by chilling fermenting wine and adding sulfur dioxide to prevent spoilage.

Working with Dr. Charles Edwards of the Washington State University/University of Idaho School of Food Science in Pullman, doctoral student Jesse Zuehlke wanted to know whether winemakers really needed the oft-recommended dose of 0.4 to 0.6 milligrams per liter of sulfur dioxide to control Brett during aging.

“There is a growing trend in winemaking now, it seems, to try and use lower amounts of sulfur dioxide,” Zuehlke said. “Part of that comes from health concerns, part of it comes from environmental concerns, and part of is just that’s how the trend is going right now.”

The research was part of a larger project investigating the relationship between temperature and sulfur dioxide in the control of Brett during wine aging. To maintain effective control of Brett, Zuehlke wanted to know if lower temperatures could maximize the effect of a reduced dose of sulfur dioxide.

Zuehlke set about investigating the correlation between the two elements, which often occur together as part of the winemaking process.

“(Winemakers) know that it reduces the likelihood of spoilage by yeast and bacteria, but no one’s really looked at it and tried to quantify exactly how much it reduces the likelihood of spoilage,” he told Wines & Vines.

The experiment
Zuehlke took three strains of B. bruxellensis originally isolated from commercial Washington wineries and subjected them to four different temperatures—10°, 15°, 18°, and 22°C. The molecular form of sulfur dioxide was added at rates of zero, 0.2, 0.5, and 1.1 milligrams per liter.

Just one of the three yeast strains was able to survive at 10°C (about 50°F), and this strain was controlled by just 0.2 milligrams per liter of molecular sulfur dioxide—or, half the minimally recommended dose (full results will be documented in a paper Zuehlke is submitting next month for publication.)

“You have a lot of different attributes of the food or the environment that will alone do a little bit to limit the growth of a yeast or bacteria,” Zuehlke said. “By putting all of those together you create a lot of small hurdles that completely stop the growth of what you’re looking at—in our case, Brettanomyces.”

The information will help winemakers better understand Brett’s behavior, and to produce wines with fewer additives.

Real-life applications
A better understanding about what controls Brett is welcomed by Joshua Maloney, director of winemaking at Milbrandt Vineyards in Mattawa, who has dealt with Brett first-hand at wineries in the past.

In addition to chilling and sulfur dioxide, he’s also found a rigorous racking schedule to be helpful in knocking down an infection and preventing the production of undesirable compounds.

“Brett lives in the bottom. And if you routinely get away from the stuff living in the bottom, if you just rack off and leave it behind, you can actually knock the population down,” he said.

This prevents the yeast population from reaching a point where it produces 4-ethylphenol and 4-ethylguaiacol, the compounds that contribute negative characters to wine. Maloney’s experience indicates that Brett strains in Eastern Washington show their nasty side at concentrations of more than 5,000 cells per milliliter.

“But below that level, particularly at 200 cells per milliliter, it generally doesn’t produce any of those nasty characters,” he said. “So, if you have Brett, and you just keep regular rackings, you keep your population low, and you keep your wine at 55°F and 35-40 parts free sulfur, you can generally avoid having any 4-ethylphenol and 4-ethylguaiacol produced.”